1. Field of the Invention
The present invention relates to flexible magnetic storage media heads, and more particularly, to an in situ radio frequency shield for a flexible magnetic storage media head.
2. Background Information
Business, science and entertainment applications depend upon computing systems to process and record data. In these applications, large volumes of data are often stored or transferred to nonvolatile storage media, such as magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical, convenient, and secure means of storing or archiving data.
Data storage technology is continually pushed to increase data storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques and decreased areal bit sizes. The data storage capacity of half-inch magnetic tape, for example, is currently measured in hundreds of gigabytes.
In linear recording media, such as magnetic tapes, data is stored on linear data tracks that run parallel to each other over the length of the tape. The magnetic tape is transferred back and forth between supply and take-up reels for reading data from or writing data to the magnetic tape, by one or more read/write heads.
FIG. 1 illustrates a traditional bidirectional, two-module magnetic tape head 100, in accordance with the prior art. As shown, the head includes a pair of bases 102 that are typically elongated “U-beams”. The bases are adhesively coupled together and a channel 104 is formed between the bases.
Each base is equipped with a module 106. Each module includes a substrate 106A in which read/write elements 108 are embedded. The modules are long enough to be able to support a tape 110 as the head steps between data tracks. A closure 106B may be added for reducing wear of the substrate. When provided, the closure 106B is adhered to the substrate using known methods.
The modules are aligned in the direction of tape travel D across the head for reading data as it is written to the tape 110. In use, the tape 110 is moved back and forth over the modules along a tape bearing surface 112 for reading and writing data on the tape.
The read/write elements alternate functionality depending upon the direction that the tape is traveling, so that a read element is downstream of a write element in the direction of tape travel. This allows data written to the tape to be immediately read back and checked for errors. The process of reading data as it is written to the tape is well known in the art as rear-while-write or read-modify-write.
A data cable 114 is bonded to each module for transferring data between the head and a controller (not shown). The data cable is typically bonded to device element pads 116 that are coupled to the read/write elements via device element leads 118 in the substrate to provide a data path between the read/write elements and controller. To bond the cable to the leads 118 of the data cable are first aligned with the device element pads that are located on the substrate. The leads are then ultrasonically welded or stitch bonded, to the pads for bonding the cable to the module. The cable then needs to be attached to the module with some form of strain relief, such as adhesively bonding the cable to the module.
However, several disadvantages are inherent in ultrasonically welding or stitch bonding. A known disadvantage of ultrasonic welding is that the leads in the cable are unsupported by the cable substrate, and extend beyond the substrate. The exposed leads are susceptible to mechanical damage which adds cost and decreases reliability of the head. A disadvantage common to both ultrasonic welding and stitch bonding, is that some form of strain relief is required, such as adhesively bonding the cable to the module. The strain relief necessitates an additional manufacturing step of the head. Another disadvantage of both ultrasonic welding and stitch bonding, is that the leads are exposed to potential shorting if an external metal RF shield is attached to the cable and placed over the leads.
Another method of bonding the cable leads to the conductive pads is anisotropic conductive film (ACF) bonding. ACF bonding uses an adhesive which has electrically conductive balls within it. The cable leads and the conductive pads on the substrate are first aligned with an ACF film sandwiched between them. The pads and leads are then pressed together at elevated temperature. This pressure results in the conductive balls being compressed to form electrical bonds between the appropriate leads and substrate pads. The conductive balls are sufficiently dense to provide electrical contact between the electrical leads and the substrate pads, while being disperse enough to avoid forming an electrical bridge between neighboring leads or pads. The elevated temperature results in the adhesive being cured to form a strong and permanent adhesive bond between the cable and the substrate.
ACF bonding provides advantages over the other noted bonding methods. With ACF bonding additional strain relief is not needed, as the adhesive in the ACF film serves the strain relief function. Further, the leads in the cable are supported by the cable substrate for reliability and inhibiting mechanically damaged cable. After ACF bonding the leads are not exposed, so the cable ground plane can extend over the leads.
A potential disadvantage of ACF bonding is that the closures are bonded using adhesives which have low glass transition temperatures (Tg). For example, one adhesive used in ACF bonding is 3M™ Scotch-Weld™ Epoxy Adhesive 2290 Amber, sold by 3M Corporation, which has a Tg of about 90° C. ACF bonding utilizes higher temperatures, and thus can heat the closure adhesive above its Tg. This can cause the closure to move relative to the substrate and become misaligned with respect to the substrate and the plane of the tape bearing surface (TBS). If the closure TBS is higher than the substrate TBS, then the magnetic field intensity measured by the readers embedded in the substrate will decrease for high density magnetic transitions written on the tape, known as Wallace spacing losses. With Wallace spacing losses, the signal decreases exponentially with the spacing between the readers and the tape surface. The write field intensity decreases similarly with distance with Wallace spacing losses.
The modules of the bi-directional read/write tape head described above are adjacent to one another. When writing data to the tape, a magnetic field is generated by one or more write elements to write the data to the tape. The radio frequency (RF) radiation of this magnetic field may be received by the read elements of the downstream module. The RF radiation received by the read elements is a source of noise that can interfere with the read elements reading the correct data from emanating the tape.
A prior art method of shielding the read elements from radio frequency radiation irradiated by the write elements, is to add an RF shield 120 between the two modules. In current computer storage magnetic tape devices, such as Linear Tape-Open (LTO) tape drives, manufactured by International Business Machines Corporation (IBM), Armonk, N.Y., a radio frequency (RF) shield 120 is positioned between the modules to reduce the amount of noise received by the read elements when writing data.
Typically, the RF shield comprises a metal foil, or sheet, and is affixed to the data cable coupled to one of the modules of the head. The RF shield is affixed to the data cable after the leads of the data cable are bonded to the device element pads on the substrate. The RF shield is positioned on the cable so that it extends into the channel between the two modules, but not above a plane of the TBS. Thus, the metal foil RF shield must be precision aligned on the cable, so that it approaches the TBS but does not protrude above the plane of the TBS. Once the foil is aligned on the cable, and thus the module, the RF shield is affixed to the cable. As can be appreciated, this process is labor intensive, and thus costly. Periodically, the RF shield is misaligned and either the costly module must be scrapped or the RF shield is realigned. Realignment of the RF shield involves pealing the adhesively bonded RF shield off the cable, which often damages the module by destroying the cable leads or causing electrostatic discharge damage (ESD) to the read devices.
Accordingly, there is a clearly-felt need in the art for a radio frequency shield for magnetic tape heads that provides sufficient RF signal blocking and is simple and cost effective to manufacture.